


Biology

by lookupkate



Category: Sherlock (TV)
Genre: Fluff, M/M, Sherlock in Love, Smut, Soulmate AU, adorable bastards, coffee shop AU, uni - Freeform
Language: English
Status: Completed
Published: 2016-04-04
Updated: 2016-04-18
Packaged: 2018-05-31 06:22:06
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 4
Words: 4,308
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/6459298
Author URL: https://archiveofourown.org/users/lookupkate/pseuds/lookupkate
Summary: <blockquote class="userstuff">
              <p>When you meet your soulmate your biology changes. It takes Sherlock a while to figure it out. It takes John even longer. Idiots.</p>
            </blockquote>





	1. Biology

**Author's Note:**

  * For [DaringD](https://archiveofourown.org/users/DaringD/gifts).



Sherlock didn't believe he had a soulmate. Some people didn't. No one knew if that meant that their soulmate had died at some point or that they were just unlucky. 

He'd seen two of his classmates meet their soulmates, something that often happened to people who stayed living in the same town they grew up in, and told himself he wasn't jealous. 

He was. He was incredibly jealous. He'd never even had a real friend. It occurred to him early on that his soulmate would have to be his friend, would possibly even want that.

But no, he was unlucky in many things and this, undoubtedly, would just be another.

_____

When you met your soulmate your biology changed. It was often something small, having to do with one of the five senses. Sometimes you would be overwhelmed by their voice. On rare occasions, people had been known to suddenly not need glasses. 

Most changes were so small that it took a while to realise what had happened.

_____

Sherlock was behind in his biology class. Not because he didn't understand, obviously, but because he couldn't bring himself to do his homework. If he'd listened when they went over the syllabus on the first day he would have known that homework, although it could be turned in at any time, was worth fifty percent of the grade.

That was how he found himself at the campus coffee shop for the eleventh day in a row, a week before the end of the semester, frantically finishing a whole semester's worth of stupidly easy work. At least the coffee was good.

He walked in at half nine and was pleased to see he was the only one there. There was no one at the counter so he rang the bell several times, expecting the mousy girl who had an internship in the morgue to come bustling out of the back with a blush and an apology. 

Instead of the girl he knew, he was surprised to find an incredibly fit bloke with blond hair and a tan. How one gets a tan in the grey weather of London, he wouldn't know.

"I said," the man repeated, "what can I get you?"

Sherlock sputtered and cursed himself for the visceral response to the man's presence. "Coffee. Large. Four sugars."

The man smiled (and wasn't that enticing?) and picked up a large mug. Sherlock couldn't stop himself from staring at the man's lips.

"Do you come to the shop often?" the man asked. He seemed to realise how much of a pickup line it was and tried again. "I'm new. I'm John."

Sherlock looked to the floor and tried to will his body into submission. Now was not the time for an erection, thank you very much. "Sherlock."

"Interesting name," John said, passing the coffee over. "Here you go. And some biscuits. On the house."

Sherlock flushed and paid, scurrying to the back of the small shop and setting up his work. Which he would have started if he hadn't tasted the coffee. It was awful.

He walked to the front and rang the bell again, this time only once. John came out from the back, eyebrows furrowed.

"This is...it's...not good," Sherlock explained clumsily.

"Oh, uh, sorry. It was the last of the pot. How about I make a new one? I'll get it to you in a minute," John replied.

Sherlock nodded and went back to try to start his homework.

He was already partway through the first assignment when John brought him the new cup.

"Advanced biology?" John asked. 

"Obviously," Sherlock said, feeling a flush take up residence once more on his cheeks.

"I took that last semester. Real pain," John said. When Sherlock simply stared at him he cleared his throat. "I'll, uh, let you get back to it."

Sherlock nodded and, when John finally turned to walk back to the front of the shop, took a sip of the freshly brewed coffee.

It was awful. Simply wretched. Bitter and cloying and worse the longer it was in his mouth.

The man may have been gorgeous, but he obviously didn't know how to make coffee. 

_____

After Sherlock left, John noticed he hadn't drank more than a sip. Curious, he picked up the cup and tried it. Cold, yes, but good. What a strange man.


	2. Coffee?

**Summary for the Chapter:**

> Leave it to Mrs Hudson to see it first.

The next night, when John saw the man walking from across the campus grounds towards the coffee shop he groaned and turned to his coworker. "Do you know this guy?"

"Which guy?" Sally asked, going up on her toes and looking over John's shoulder.

"That one," John said, tipping his chin towards Sherlock. "The one that smells like vanilla."

"Smells like..." Sally said, confused, "yes, I know him. He's a pain in the arse. Don't know about the vanilla, though."

"Last time he came in he complained about the coffee," John admitted.

Sally snorted. "That's about the ONLY thing he doesn't complain about. What on earth did you do to it?"

"No clue," John replied. "I tried it when he left and it was fine."

"He's picky," Sally said, crossing her arms. "Take his order and I'll make it. If he complains again we'll know he's full of shit."

John bristled at the thought that Sally didn't believe his own account of the coffee the night before, but let it go. Sally was fairly easy to work with so he went about wiping down the counter as Sherlock walked in.

"Black, four sugars?" he asked as Sherlock came up to the counter.

The man fumbled his wallet and nodded, passing over some cash and shifting his rucksack to his other shoulder as he waited for his change. Sally came over with the steaming mug and gave him a fake smile. He nodded and walked to the back of the shop, getting his things out and starting his homework.

"You didn't smell that" John asked. "Sort of peculiar for a man to wear vanilla. Reminds me of the biscuits my mother used to make."

"You've lost your marbles, mate," Sally said with a small grin.

John frowned at her.

"You're smitten," she explained. "Gross."

_____

The coffee that night was completely awful. Just as bad as the first. Sherlock blushed a few times as John tried to flirt with him and then left two hours later without taking a second sip.

When he got home Mrs Hudson was still awake, hoovering the entryway.

"Oh, Sherlock, dear. Help me move my sofa, will you?" she asked as he walked in.

Sherlock followed her into her flat. "What on earth are you doing up?"

"The hip. Can't seem to stay asleep," she explained.

He helped her move things and replaced a burned out lightbulb and then they sat for tea.

"I know you prefer coffee, but I can't have you playing that violin of yours until the early morning," she said, pushing over a plate of biscuits and pouring some tea.

"I normally do," Sherlock said, looking a bit perplexed.

"But?" She pressed, taking a seat across from him and sipping primly.

"But I can't seem to get a good cup. I would swear it was because of the new barista but his coworker made mine tonight. Used to be my favorite place but now the coffee is just terrible," Sherlock said, sulking a bit.

Mrs Hudson eyed him. It couldn't be. It probably wasn't, and yet...

"Anything else taste off?" she asked, going to the kitchen and pressing the button on her new single-cup coffee machine. (Really a savior for those who live alone.)

Sherlock took a bite of his biscuit and shook his head "No."

A few minutes later, minutes he spent in deep contemplation, Mrs H retuned to the table and set a cup of coffee down in front of him.

"I thought you said I couldn't have this much caffeine," he said, spooning sugar into his mug and stirring.

"Just try it, love," she said.

Sherlock watched her with some suspicion but took a sip anyhow. His lip curled and he took a quick gulp of his tea. She grinned at him.

"What on earth are you so excited about? That you forgot how to make a decent cup of coffee, or that you forgot to rinse the soap from this mug?" he demanded, feeling a little embarrassed, thought he wouldn't admit it.

"Nothing dear," she tutted. "Drink your tea."


	3. God Yes

When Sherlock came to the realization it was two weeks later. He wasn't sure why he kept going back to the coffee shop, ordering tea, as coffee had somehow stopped tasting good no matter where it was made, but he found himself here every night. He'd just entered the coffee shop and was waiting behind a rare patron when it hit him.

Taste.

Taste was a common one. He pulled out his mobile and started to sift through stories of people's tastebuds acting strange when they met their soulmate. Why he hadn't heard it theorized that what changed would be something you consume a great deal of probably had more to do with deletion than anything else. He'd never assumed that he'd need to know anything about soul mates.

"Sherlock, you in there?" John asked, smiling at the man who'd charmed him so.

"What is your favorite thing to eat?" Sherlock asked, then rethinking, "scratch that, what is the thing you eat the most of."

John chuckled and leaned against the counter between them, sticking his tongue out a bit and looking up in thought. "Dunno. Tea probably. Does that count as eating?"

Sherlock smiled and ordered a tea, John thinking how peculiar the man was acting. Sherlock had been clearly smitten for a while now, but he was always soft spoken and had trouble looking John in the eye. When he did speak it was gruff state of fact, not this curious thing he was doing now. 

John started to pass the tea over and Sherlock held his hand out. "Try it."

"I don't drink it without milk," John said, eyebrows furrowing.

"Doesn't matter. Well, as long as my hypothesis is right," Sherlock replied, pushing the tea closer to John and watching him raptly.

John held the tea to his lips, blowing on the surface for a moment, and then took a sip. Sherlock grinned at him as he winced and set the cup down.

"Well?" Sherlock asked, practically bouncing.

"Too hot to drink just yet," John said, nose scrunched up, "and needs milk."

Sherlock forgot how to breathe, realising for the first time that he had wanted that to be the answer, that he had wanted this man he barely knew to be his soulmate.

"Is that, sorry, was that not what you were hoping for?" John asked, pulling him from his thoughts.

"Unfortunately, no," Sherlock said, taking the tea and paying.

"Sorry about that," John said just as Sherlock was turning to go to the back of the room.

Sherlock turned back to him, looking him up and down quizzically. "Why would you be sorry?"

"I don't know," John answered, truthfully. "I suppose you just looked happy. I don't think I've ever seen you happy. It was...nice."

Sherlock blushed and ducked his head, mumbling something before walking to the back of the room. John grinned at him and went about cleaning the counter absentmindedly.

_____

About an hour later a drunk student shouted through the large plate glass window and stumbled in. John was already on alert, but Sherlock seemed not to notice, too busy in his own head.

"Oi, prick," the man shouted, moving clumsily between chairs towards the back of the room.

John swiftly cut him off, standing between the man and Sherlock. That caught Sherlock's attention and enraged the man.

"You told my girlfriend I'm cheating on her!" the man shouted, pointing at Sherlock.

Sherlock replied as if it shouldn't have offended the man. "You are."

The man reached for Sherlock and John struck him with his shoulder, knocking him to the ground. "Get out. Now."

The man stood and tried to hit John, John deflecting the hit and landing one of his own. The crunch of the man's nose was enough to make everyone wince. Luckily, the man left before they could get into even more of a fight. John didn't think he'd be able to explain away a broken window to his boss.

When the man was out of sight Sherlock rushed to John and inspected his fist, mumbling to him and dragging him to the front to wash it. "Obviously not your blood. You're absolutely mad. Never had anyone stick up for me."

John, full of adrenalin with nowhere to go, spoke loudly.

"You're impossible," he blurted, "and a bloody mess. Christ, what did you say to that guy's girlfriend?"

"She came to me with a proposition," Sherlock explained, cleaning and drying John's hand. "She would let me copy her astronomy notes for the final if I found out whether or not her boyfriend was cheating on her. He was cheating on her and I told her as much. And you...you hit him. I'm sure that's worse than me telling her the truth."

"Hey, I was sticking up for you," John said, pulling back.

Sherlock panicked and took a step forward. "No, it was, it was good. No, I meant, thank you."

John's lips pursed and he shrugged. "It's alright. Not like I couldn't handle him."

"Rugby player. I'd say team captain, but your fierce determination to be a surgeon, and to pay off your schooling, wouldn't allow for enough time. I'm sure you'd make a good captain," Sherlock said quickly.

John grinned and shook his head. "Have you been watching me play?"

Sherlock swallowed and looked to the ground. "Simple deduction. Your physicality and tan, the way you took the man down. I saw some of the books in your rucksack, the other day as well, too advanced for your year, yet there you are, muddling through them. They were bought second hand, as was your phone. You only have one pair of nice trousers and you get cheap haircuts. Your family can't pay for school if they can't afford to help you along with haircuts."

For a second Sherlock thought he was about to be the next victim of one of John's sound left hooks, then John smiled.

"That's absolutely brilliant."

"Really?" Sherlock asked, not at all expecting the response.

John chuckled and ran a hand through his hair self-consciously . "God yes, how on earth did you do that?" 

"It's a bit difficult to explain," Sherlock said, swallowing hard and looking to the floor.

"Let me," John said, pausing and clearing his throat, "let me take you out. You can explain it over late night Chinese."

Sherlock looked up, eyes wide, and nodded, forgetting completely that John Watson was apparently not his soulmate.


	4. Vanilla

**Summary for the Chapter:**

> Happily ever after. As promised.

John and Sherlock met the next night at a Chinese place Sherlock suggested. It was one of those hole-in-the-wall places that you'd miss if you didn't already know where it was. On the front of the building was a simple red door, yet it opened onto a large room with ornate decorations and a pane glass window that looked out on a gorgeous little garden of sorts. They sat across from each other, not sure who should speak first, and waited for a menu.

"Sherlock Holmes," the waiter said as she approached, "it's so good to have you back!"

John's forehead scrunched up as the woman told them they could have anything they wanted, on the house, and that she'd bring out some tea and baijiu. When the woman left John finally had something to say.

"You know her?" he asked in a stage whisper.

"I know the owner," Sherlock corrected, hating the flush that took to his neck. "Helped her find the man who robbed them when the police were of little help."

"Really?" John asked, grinning.

"Mmm," Sherlock agreed. "Hobby of mine."

"Catching robbers?" John asked as the tea and baijiu was brought their way.

Sherlock smiled softly and looked up at John from beneath his eyelashes as if the next line was some sort of flirtation. "All sorts of criminals."

John sat back in his seat and laughed. "How? With that thing you did? The bit where you could tell the bloke was cheating?"

"Deductive reasoning. One of my techniques. In this case everything came down to the soil in the rug beneath the window. Interesting composition, and one that could only be found in a certain part of town. Once I knew that, it was only a matter of tobacco ash," Sherlock explained.

"Tobacco ash?" John asked, taking a sip of his tea.

Sherlock nodded and picked up the small cup of baijiu with his rather large fingers, the size of the cup making them appear even larger. "People are particular about their brand of cigarettes."

"You really are a genius, aren't you?" John asked with a deep sigh, smile going lopsided.

Sherlock simply blushed and nodded.

_____

It took another date, this time at an equally small pizza shop, for John to get up the nerve to kiss Sherlock. They'd made it up to his flat, his roommate out for the night, and were sitting on the sofa watching a movie. They were also holding hands. That was very nice, very nice indeed.

"That can't possibly be right," Sherlock complained. "They haven't used that medication to treat infections that bad in a decade. Don't the idiots that write this droll know how to make a simple Google-"

John, overcome with affection for the man, leaned in and shut him up with his lips. Sherlock startled and held his breath for a moment before slumping down a bit and letting John run his fingers through his curls.

"You're adorable," John teased as he pulled away to look Sherlock in the eye.

"B-because I refuse to overlook their stupidity?" Sherlock asked, completely flummoxed and leaning back in to get more of John's lips.

"Mmm," John agreed against his mouth, licking into it and moaning before pulling away again. "Christ, you even taste like vanilla! How do you do that?"

Sherlock stilled and looked rapidly back and forth between John's eyes. "I'm not sure what you mean."

"The, the cologne you wear," John explained, feeling dizzy and gripping Sherlock's hair so he could breathe in against his neck. "Vanilla."

"I don't wear cologne," Sherlock said, eyes far off.

John growled and licked Sherlock's neck, moaning as he did and sucking greedily. Sherlock made a high pitched whinge and John drew back.

"Vanilla. You taste like vanilla. Body wash? Shampoo?" John asked, not giving Sherlock a chance to answer as he pulled him back in for a hungry kiss.

Sherlock's brain felt like it was short-circuiting. He couldn't seem to pull the thought out that was slowly forming. Something, something about what John was saying was incredibly important, but all the blood in his entire body was rushing to his cock and he'd only ever done this with one other person and John was pulling back again and that was decidedly not what he needed.

He panted and pulled his shirt off, climbing into John's lap and kissing him again. Now that the flood gates were open, it seemed, Sherlock was far from nervous. John was just fine with that.

John let Sherlock lick into his mouth and pull at his hair a while longer before pulling his own shirt over his head and tossing it to the side, sighing as their chests pressed together and Sherlock started to roll his hips. It was hot, their proximity and movement making sweat bead between John's shoulder-blades, and desperate.

"Christ, you feel good," John said, gripping Sherlock's hips and pushing up into him, his cock begging for more pressure and friction.

"This is," Sherlock whined, "this is...this..."

"You're so beautiful," John murmured, sucking again at Sherlock's neck. "So beautiful."

Sherlock rocked against him and sucked on his bottom lip and soon they were coming in their pants and kissing more slowly. That thought, though, wouldn't come to fruition in Sherlock's mind.

_____

Sometime between John asking Sherlock to be his boyfriend and them moving in together a month later Sherlock realised that John didn't really seem to believe in soulmates. It made sense, if you looked back on his family life, but was unfortunate as John was obviously Sherlock's. If the coffee didn't convince Sherlock, the thing about vanilla did. Even Mrs Hudson seemed to notice how close they were.

They lived together comfortable for a month and a half before it was brought up, although John had professed his love at month two. How, after all, do you convince a non-believer?

They have to come to it on their own.

_____

John was sitting in class, diligently taking notes, when the subject was brought up. He'd thought it would be tackled as side note. It very much wasn't.

"Who in this class has met their soulmate?" the professor asked, raising her own hand and looking around as fifteen percent of the class did as well. "Good. Now, who would like to tell us about how you knew?"

A girl near the front kept her hand raised and the teacher called on her. Her story of changing tastes and strong scents had John first scratching the back of his head and then, after it all started to click into place, sitting with his mouth hanging open.

_____

When Sherlock finally came home that night, after snagging some time in his favorite lab, John was sitting with a cold cup of tea at the kitchen table. He was staring at the sink in a way that made Sherlock decidedly uncomfortable.

"John," he asked, setting his rucksack down carefully instead of slinging it off like usual.

John took a deep breath and looked up to him, eyes almost sad. "How long have you known?"

"W-what do you mean?" Sherlock asked, spinning through their recent arguments for anything that John would find this upsetting. 

"You're a genius. You're a genius and it affected you first, so you must have known. Well, I suppose it affected us at the same time, didn't it? That's how it works. But you, you noticed it right away. That's why...that's why you kept coming to the shop once you stopped liking coffee, isn't it?" John said quickly, eyes flitting around the room as if Sherlock's presence was all he needed to figure it out.

"John," Sherlock said, now feeling rather foolish for not bringing it up.

"Did you know before I told you I loved you?" John asked, standing suddenly and taking a step towards Sherlock.

"Y-yes," Sherlock sputtered.

John nodded once and looked at the floor. "But you seemed...you hesitated, saying it back."

"I've never been in love before," Sherlock admitted. "Please, please don't be angry with me."

John looked up at him and brought his hand up to Sherlock's shoulder. Sherlock glanced over at it and then back at John.

"Why didn't you tell me?" John asked softly.

"You wouldn't have believed m-me!" Sherlock said, all the emotions of thinking he'd met his soulmate and having that torn away and then getting it back flooded him. He could feel the tears leaking from his eyes.

John pulled him to the sofa and stroked his hair. "Hey, I'm not angry. I'm surprised, that's all. I guess I just didn't think-" Sherlock let out a choking sob against his chest and John kissed his curls.

Sherlock settled with John's soft attention and they were soon brought back to kissing. It was slow and loving as John ran his fingers through Sherlock's hair. When he started giggling into Sherlock's mouth, the genius drew back to look at him questioningly, face mottled and streaked with tears.

"Sorry," John said, trying to reign the laughter in, "sorry. I was just thinking about when we met. I thought you were full of shit about the coffee."

Sherlock started laughing with him and chewed his lip. "It was really horrid."

"I've ruined coffee for you, then?" John asked, giggling harder.

Sherlock grinned, lopsided and gorgeous. "I'm afraid so."

"However can I make it up to you?" John asked, smile turning suggestive.

Sherlock blushed and shrugged. "I don't know. What did you have in mind?"

John pushed him back onto the sofa and started in on his trousers. Sherlock did his best to assist as his mind spun, lifting his hips and legs in turn so John could pull his trousers and pants off completely. 

John.

John was his soulmate. How on earth had that-

His thoughts came to a stumbling stop as John took his cock in hand and stroked it as he lipped at the head. John saw that happen, saw Sherlock's attention shift to him, and grinned, licking at his prick and taking the head into his mouth.

"Oh, God," Sherlock moaned, head falling back as John took in more and more of his shaft.

He set up a bruising rhythm, desperate to tear Sherlock to pieces and make him come as quickly as possible. He wanted to wring him dry and crawl into bed with him and hold him. God, how he wanted to hold him.

Sherlock continued to moan as John sucked at just the tip of his prick, tongue playing with the foreskin and hand stroking his shaft with just enough pressure. 

Soon, Sherlock was coming, breathing in short gasps. John fumbled with his belt and pulled his own cock out, stroking it and promptly staining the sofa.

_____

Later that night, in bed and dozing off, John proposed. 

They were married in six months and two years later they became Dr and Mr Watson. 

Happily ever after? Yes, that too.


End file.
